Interleukin-6 and Cardiovascular Events in Healthy Adults

Background Elevated interleukin (IL)-6 levels have been linked to adverse outcomes in patients with and without baseline cardiovascular disease (CVD). Objectives The purpose of this study was to examine the association between circulating IL-6 levels and CVD events without baseline CVD across racial and ethnic groups. Methods We conducted an observational analysis utilizing the MESA (Multi-Ethnic Study of Atherosclerosis), a multicenter, prospective community-based study of CVD at baseline from four racial and ethnic groups. IL-6 levels were measured at the time of enrollment (visit 1) and were divided into 3 terciles. Patient baseline characteristics and outcomes, including all-cause mortality, CV mortality, heart failure, and non-CV mortality, were included. Cox proportional hazard regression models were used to assess associations between IL-6 levels and study outcomes with IL-6 tercile 1 as reference. Results Of 6,622 individuals, over half were women (53%) with a median age of 62 (IQR: 53-70) years. Racial and ethnic composition was non-Hispanic White (39%) followed by African American (27%), Hispanic (22%), and Chinese American (12%). Compared to tercile 1, participants with IL-6 tercile 3 had a higher adjusted risk of and all-cause mortality (HR: 1.98 [95% CI: 1.67-2.36]), CV mortality (HR: 1.55 [95% CI: 1.05-2.30]), non-CV mortality (HR: 2.05 [95% CI: 1.65-2.56]), and heart failure (HR: 1.48 [95% CI: 0.99-2.19]). When tested as a continuous variable, higher levels of IL-6 were associated with an increased risk of all individual outcomes. Compared to non-Hispanic White participants, the unadjusted and adjusted risk of all outcomes across all races and ethnicities was similar across all IL-6 terciles. Conclusions High levels of circulating IL-6 are associated with worse CV outcomes and increased all-cause mortality consistently across all racial and ethnic groups.

I nterleukin (IL)-6 is an immune- mediated, pro-inflammatory cytokine that is elevated in systemic inflammatory states. 1 IL-6 plays a direct role in activating endothelial monocytes and macrophages, thereby accelerating plaque accumulation and atherosclerosis. 2,35][6] As a result, there are ongoing trials into novel therapies aimed at inhibiting circulating IL-6 for the reduction of CVD events, including the ZEUS ( NCT05636176). 7,8ere may be differences in baseline levels of IL-6 and strength of association with CVD outcomes across different races and ethnicities.In a cohort of patients with baseline chronic kidney disease, African American individuals had significantly higher levels of circulating IL-6 levels compared to Mexican American and non-Hispanic (NH) White individuals. 9Barrow et al also found significantly higher IL-6 levels in Black adults compared to White adults; however, the association between circulating IL-6 and CV mortality was stronger among White adults compared to Black adults. 10Similar evidence for the association of IL-6 levels with CVD outcomes in individuals without clinical CVD is less well-established.Cainzos-Achirica et al evaluated the prognostic implications of IL-6 levels on hard coronary heart disease (CHD) events, stroke, hard atherosclerotic CVD, and incident heart failure (HF) in patients without clinical CVD using the MESA (Multi-Ethnic Study of Atherosclerosis); however, the analysis was focused on assessing differences between users and nonusers of statins and did not assess the impact of race and ethnicity on clinical outcomes. 11It is pertinent to assess outcomes in the context of differences in circulating IL-6 across races and ethnicities to better understand overall population-level risk of CVD and identify high-risk cohorts that would potentially benefit from anti-IL-6 therapies.In this study, we utilized patient-level data from the MESA cohort to examine the association between circulating IL-6 levels and the occurrence of CVD events in individuals without clinical CVD at baseline and evaluated for the presence of effect modification across different racial and ethnic groups.The details of the MESA study have been reported

METHODS
elsewhere 12 and also available on the study website  tively.Baseline use of antihypertensive agents was most common (37.0%), followed by aspirin (25.0%),
CV OUTCOMES.A l l -c a u s e m o r t a l i t y .The unadjusted overall incidence of all-cause mortality was 14.5 per 1,000 (IQR: 13.7-15.3)person-years.
Individuals in IL-6 tercile 3 had a higher risk of allcause mortality compared to individuals in tercile 1 (adjusted HR: 1.98 [95% CI: 1.67-2.36]).When tested as a continuous variable, higher IL-6 levels were associated with a higher risk of all-cause mortality in both unadjusted and fully adjusted models (Supplemental Table 1, Figure 1).Crude Kaplan-Meier survival estimates indicate significantly lower cumulative probability of survival with early divergence of survival curves for IL-6 terciles 2 and 3, compared to tercile 1 (log rank P < 0.001) (Figure 2).When tested as a continuous variable, higher IL-6 levels were associated with a higher risk of CV mortality in both unadjusted and fully adjusted models (Supplemental Table 1, Figure 1).
N o n -C V m o r t a l i t y .The unadjusted overall incidence of non-CV mortality was 10.9 per 1,000 (IQR: 10.2-11.7)person-years.Individuals in IL-6 tercile 3 had a significantly higher risk of non-CV mortality compared to individuals in IL-6 tercile 1 (adjusted HR: 2.05 [95% CI: 1.65-2.56]).When tested as a continuous variable, higher IL-6 levels were associated with a higher risk of non-CV mortality in both unadjusted and fully adjusted models (Supplemental Table 1, When tested as a continuous variable, the risk of HF with CVD did not increase with increasing IL-6 levels (Supplemental Table 1, Figure 1).A competing risk analysis using all-cause mortality yielded similar associations (Supplemental Table 2).A cumulative incidence analysis for incident HF across the IL-6 terciles using competing risk regression is provided in Figure 3.

DISCUSSION
The study reveals several key findings.Patients with higher IL-6 levels were more likely to be older, female, current smokers; had hypertension, diabetes, and a family history of CHD; had a higher median systolic blood pressure, heart rate, and waist circumference; and included a larger proportion of African American and Hispanic individuals compared to those with lower IL-6 levels.Consistent with prior meta-analyses, 13 in this multiethnic cohort, elevated IL-6 levels were consistently associated with a higher incidence of all major CVD outcomes even after  CV ¼ cardiovascular; IL-6 ¼ interleukin-6; NHW ¼ non-Hispanic White.
Khan et al

Interleukin-6 and Cardiovascular Outcomes
A U G U S T 2 0 2 4 : 1 0 1 0 6 3 adjustment for a broad range of clinical covariates, with no major difference in outcomes across race and ethnicities (Central Illustration).
These findings from a prospective cohort of closely followed patients with average baseline risk of CVD further strengthen the prognostic role of circulating IL-6 in mediating atherosclerotic CVD risk.A prior analysis from the MESA cohort reported similar findings over a follow-up of 10 years and focused on individual components of atherosclerotic CVD and all-cause death stratified by user and nonusers of statins, whereas our study additionally evaluated association between IL-6 and non-CVD events including mortality and HF. 11Evidence from genetic studies has demonstrated a potentially causal role of IL-6 in the development and the acceleration of atherosclerosis. 3,14IL-6 signaling is also implicated in coronary and peripheral arterial disease, and formation of aortic aneurysm, independent of established risk factors suggesting significant direct effects on systemic arterial vasculature associated with circulating IL-6. 6,15,16Ridker et al previously reported that healthy men with elevated baseline IL-6 levels had a higher risk of development of myocardial infarction compared to an age and smoking status matched cohort even after adjustment for other CVD risk factors. 6In further prospective nested casecontrol analysis, the same group found baseline circulating C-reactive protein (CRP) and IL-6 levels to be a strong predictor of adverse CVD events in healthy men, and circulating CRP, which is considered a surrogate to circulating IL-6 levels, 17 in healthy women. 18,19e association between elevated IL-6 levels and incident HF is another important finding of our study.
Prior analysis from the MESA cohort revealed that Interleukin-6 and Cardiovascular Outcomes high circulating IL-6 levels are related to a reduced regional left ventricular systolic function in apparently healthy individuals 20 and are associated with increased risk of incident HF. 11 Studies have consistently reported an increased risk of incident HF in patients with high IL-6 levels, with the association mostly attributed to HF with reduced ejection fraction, 21 although some studies have reported a higher risk of HF with preserved ejection fraction. 22,23 patients with prevalent HF and preserved ejection fraction, those with increased IL-6 display greater body fat, particularly visceral fat, 24 and the present data extend this relationship to patients without apparent CVD in MESA.
We also found a significant association between high circulating IL-6 levels and all-cause mortality in a healthy, relatively young cohort (median age w62 years).This indicates that a pro-inflammatory state even in younger adults with average CVD risk leads to worse outcomes. Lindmark et al found an increased risk of all-cause mortality in patients with elevated IL-6 levels and unstable coronary artery disease and reported a mortality benefit with early invasive management in those with high IL-6 levels. 5It can be postulated that elevated IL-6 levels in healthy adults can allow for identification of a high-risk cohort that may benefit from more aggressive preventive interventions.
This analysis was conducted in a large group of racially and ethnically diverse population with a high representation of African American participants (27%) and Hispanic participants (22%) in this study.We found that there was an increasing proportion of Hispanic and African American adults from IL-6 terciles 1 to 3, with both racial and ethnic groups constituting 60% of the tercile 3 group, and a corresponding decrease in NH White adults and Chinese American adults. 9,26Prior evidence suggests that the differential levels of IL-6, especially in African American individuals, might be partly explained by higher body mass index which is independently correlated with circulating IL-6 levels. 9Current analysis also demonstrated higher body mass index and waist circumference in patients with higher circulating IL-6 levels (Table 1).The unadjusted and adjusted risk of all CV outcomes across all races and ethnicities was similar across all IL-6 terciles.These data suggest that adults from all races and ethnicities with elevated circulating IL-6 levels are at higher risk of most CVD events, despite some racial and ethnic groups (African American and Hispanic participants) having higher circulating IL-6 levels.Prior studies have not specifically explored these associations.Jia et al assessed the association of IL-6 and IL-18 and development of CVD events in the ARIC (Atherosclerosis Risk In Communities) cohort, which is also a racially and ethnically diverse prospective cohort and found that IL-6 levels were related to higher CVD event rate independent of elevation other inflammatory markers like high-sensitivity troponin, natriuretic peptides, and CRP. 27ese findings confirm that inflammatory markers like IL-6 may have utility in predicting risk of CVD events in average-risk populations and are a potential target for therapeutic agents to prevent CVD events.
There is no current clinical consensus or guidance on the routine use of IL-6 testing for risk stratification and prognostication for any age group.Most studies have been performed in middle age to elderly patients where elevated circulating IL-6 levels have positively correlated with an increased risk of worse outcomes.There has also been a growing interest in anti-inflammatory therapies to reduce the risk of adverse CVD events in patients with established CVD.
Low-dose colchicine, a drug that inhibits inflammatory pathways upstream of IL-6 in the cytokine cascade, was found to reduce the risk of adverse CVD events in patients with coronary artery disease 28,29 and has been approved for secondary prevention among patients with atherosclerotic disease. 30In the CANTOS (Canakinumab Anti-Inflammatory Thrombosis Outcomes Study) of IL-1 inhibition in patients with prior myocardial infarction, patients with more robust reductions in IL-6 had greater CV benefit from targeted anti-inflammatory therapy. 318][9] Therefore, the finding TRANSLATIONAL OUTLOOK: Elevated levels of circulating IL-6 have consistently shown an association with a higher risk of CV events in apparently healthy individuals.Racial and ethnic differences have historically influenced the population-level prevalence of CV disease; however, these differences do not significantly modify the association between baseline IL-6 levels and risk of future CV events.
Further evaluation is warranted to explore IL-6 as a therapeutic target to reduce the risk of CV events in high-risk and healthy individuals.

Interleukin-6 and Cardiovascular Outcomes
A U G U S T 2 0 2 4 : 1 0 1 0 6 3 STUDY DESIGN.The MESA is a multicenter, National Heart, Lung, and Blood Institute-funded, communitybased cohort study of apparently healthy men and women without clinical CVD (eg, myocardial infarction, stroke, peripheral artery disease, HF, chronic kidney disease) at baseline from four racial and ethnic groups recruited in 6 sites within the United States.

(
https://www.mesa-nhlbi.org).The MESA study was approved by the respective Institutional Review Boards at each participating site, and individual informed consent was taken from all participants.STUDY POPULATION.All participants evaluated in MESA visit 1 were included (N ¼ 6,814).Of 6,814 participants, those with missing information or unmeasured IL-6 were excluded.Finally, 6,622 patients with no CVD at baseline were included.EVENT ASCERTAINMENT.Patient characteristics obtained at baseline were recorded.Participants were contacted every 9 to 12 months to inquire about CVD outpatient diagnoses, hospital admissions, and procedures.CV mortality was defined as death due any atherosclerotic disease, stroke, CHD, and other CVD.Deaths not attributed to aforementioned were considered as non-CV mortality.HF was defined by the presence of symptoms suggestive of the disease A B B R E V I A T I O N S A N D A C R O N Y M S CHD = coronary heart disease CRP = C-reactive protein CVD = cardiovascular disease HF = heart failure IL = interleukin NH = non-Hispanic Medicine, University Hospital Centre, Zagreb, Croatia; i Duke-NUS Medical School, Singapore, Singapore; j Institut de Cardiologie, de Montréal, Université de Montréal, Montréal, Québec, Canada; k Department of Cardiology, University Medical Center of Groningen, University of Groningen, Groningen, the Netherlands; l Heart, Vascular, and Thoracic Institute, Cleveland Clinic, (eg, shortness of breath, edema), a clinician diagnosis, and use of medical therapy for HF.

C
V m o r t a l i t y .The unadjusted overall incidence of CV mortality was 3.79 per 1,000 person-years (IQR: 3.39-4.25).Individuals in IL-6 terciles 3 had a higher risk of CV mortality compared to individuals in IL-6 tercile 1 (adjusted HR: 1.55 [95% CI: 1.05-2.30]).

FIGURE 1
FIGURE 1 Cox Proportional Hazard Models Comparing the Risk of Cardiovascular Outcomes Across IL-6 Terciles

FIGURE 2
FIGURE 2 Kaplan-Meier Estimates for Patients With IL-6 Levels in Terciles 1 to 3 for All-Cause Mortality

J
A C C : A D V A N C E S , V O L . 3 , N O .8 the interaction analysis between racial and ethnic groups and outcomes across IL-6 terciles.The adjusted risk of CV mortality was similar for African American and Hispanic participants compared to NH White participants across all IL-6 terciles (P > 0.05 for all).Non-CV mortality was similar among African Americans and NH White participants across all IL-6 terciles, whereas Hispanic participants had a lower risk of non-CV mortality in tercile 1 and 2 on unadjusted analysis with no statistical significance in tercile 1 on adjusted analysis (P ¼ 0.14).The risk of overall HF was not significantly different among African American and Hispanic participants compared to NH White participants across all IL-6 terciles on both unadjusted and fully adjusted analyses.Additionally, the risk of all-cause mortality was similar among African American and Hispanic participants compared to NH White participants on both unadjusted and fully adjusted analyses.

FIGURE 3
FIGURE 3 Cumulative Incidence Estimates for Patients With IL-6 Levels in Terciles 1 to 3 for Incident Heart Failure

CENTRAL ILLUSTRATION Interleukin- 6 and
Cardiovascular Events in Healthy Adults Khan MS, et al.JACC Adv.2024;3(8):101063.Diagrammatic overview of the baseline characteristics, association of overall clinical outcomes with il-6 terciles, differences across races and ethnicities, and kaplan-meier estimates for all-cause mortality for patients with IL-6 levels in terciles 1 to 3. IL ¼ interleukin.J A C C : A D V A N C E S , V O L . 3 , N O .8

18.
of a strong association between CVD outcomes and IL-6 levels across all races and ethnicities in this study further underscores the importance of the development of targeted therapies to improve outcomes across a large group of patients with CVD.STUDY LIMITATIONS.This study has certain limitations.The MESA registry only recorded circulating IL-6 levels at enrollment, so our analysis does not account for longitudinal variations in circulating IL-6Khan et alJ A C C : A D V A N C E S , V O L .3 , N O .8 Ridker PM, Cushman M, Stampfer MJ, Tracy RP, Hennekens CH.Inflammation, aspirin, and the risk of cardiovascular disease in apparently healthy men.N Engl J Med. 1997;336:973-979.19.Ridker PM, Hennekens CH, Buring J, Rifai N. Creactive protein and other markers of inflammation in the prediction of cardiovascular disease in women.N Engl J Med. 2000;342:1066-1067.20.Yan AT, Yan RT, Cushman M, et al.Relationship of interleukin-6 with regional and global leftventricular function in asymptomatic individuals without clinical cardiovascular disease: insights PERSPECTIVES COMPETENCY IN MEDICAL KNOWLEDGE: In this evaluation of the MESA cohort, we examined the association between circulating IL-6 levels and CV events in an ethnically diverse cohort of apparently healthy adults.Participants with higher baseline IL-6 levels had a significantly higher risk of all-cause mortality, CV mortality, non-CV mortality, and HF, with little effect modification across racial and ethnic groups.
Khan et alJ A C C : A D V A N C E S , V O L . 3 , N O .8 , 2 0 2 4

TABLE 2
Cox Proportional Hazard Model and P Value for Interaction in African American and Hispanics Adults With Reference to Non-Hispanic Whites a Model 1 was crude (unadjusted).b Model 2 adjusted for age at baseline, sex, race/ethnicity, current smoking, family history of CHD, waist circumference, systolic blood pressure, total cholesterol, HDL cholesterol, LDL cholesterol, diabetes, hypertension, aspirin use, antihypertensive medication use, insulin use, statin use, troponin T, and NT-proBNP (all assessed at baseline).